The present invention relates to an image processing apparatus, method and system for performing color matching that takes lighting characteristics into consideration.
In a conventional CMS (Color Management System), color matching is implemented by using a device-independent color space, such as an XYZ or L*a*b* color system defined by the CIE (International Committee for the study of Lighting and Color). This color matching is based upon the idea that if two colors are described by identical coordinates in the same color space, then the appearance of the two colors will match. However, the assurance of color matching in this color space is premised on the fact that both of the compared color images are observed under identical lighting conditions.
Recently, CIECAM97s (CAM stands for Color Appearance Model) has been proposed by the CIE as a new color system that solves the above problem. An example of color matching based upon this color system is shown in FIG. 8. It will be understood from FIG. 8 that an output image Xr, Yr, Zr that is the result of correcting a disparity in lighting conditions is eventually obtained by inputting lighting conditions with respect to tristimulus values X, Y, Z of an input image indicated by xe2x80x9cSamplexe2x80x9d at the top center of the diagram, where the lighting conditions are lighting conditions (indicated on the right side) for observing the input image and lighting conditions (indicated on the left side) for observing the output image.
The lighting conditions in this color system have the following as parameters: relative tristimulus values Xw, Yw, Zw of the illuminating lamp, luminance La of the adaptation visual field (a value which is 20% of the absolute luminance of the adaptation visual field), and relative luminance Yb of the background (reflectivity of N5 in the Munsell color system). In FIG. 8, xe2x80x9crxe2x80x9d is appended to the end of the parameters of the lighting conditions for observing the output image.
Generally, in order to implement the color matching shown in FIG. 8 in a color management system that uses CIECAM97s, a viewing condition tag that stores the characteristics of lighting conditions is provided in a device profile that is based upon the ICC (Inter Color Consortium) format, and color conversion processing in accordance with these lighting conditions is executed.
In a case where color matching using CIECAM97s is thus carried out, it is necessary to detect the parameters (characteristics) of the lighting conditions simply and accurately, and methods of performing such detection have been proposed.
For example, the specification of Japanese Patent Application Laid-Open No. 11-232444 discloses a method (simple setting method) in which any one of a plurality of profiles prepared in advance by limiting luminance and color temperature as observed lighting conditions is selected sensorially by the user employing the user interface of utility software.
In another example, the specification of Japanese Patent Application Laid-Open No. 9-214787 discloses a method (photometric sensor method) in which the characteristic values of lighting conditions are sensed directly by a photometric sensor.
However, the conventional methods of detecting lighting conditions involve certain problems. Specifically, with the conventional simple setting method, the lighting conditions that can be selected are limited to several types and a sensorial selection is made by the user. As a consequence, an error develops between these characteristic values and the characteristic values of the actual lighting conditions and detecting accurate characteristic values is not possible.
The photometric sensor method, on the other hand, is superior in terms of detection precision but the sensor apparatus is complicated in structure and lacks simplicity.
The present invention has been proposed to solve the problems of the prior art and has as its object to provide an image processing apparatus capable of detecting, simply and accurately, lighting characteristics used in color matching processing that employs a color appearance model.
According to the present invention, the foregoing object is attained by providing an image processing method for executing correction processing using a color appearance model, comprising: a rated-product number input step of inputting a rated-product number of a lighting lamp; a lighting characteristic calculation step of calculating lighting characteristic values based upon the rated-product number; and a correction step of executing correction processing that uses a color appearance model that is based upon the lighting characteristic values.
Another object of the present invention is to so arrange it that appropriate color matching processing can be executed in conformity with detected lighting characteristics.
According to the present invention, the foregoing object is attained by providing an image processing method for executing correction processing using a color appearance model, comprising: an input step of inputting illumination-light source conditions and indoor lighting environment conditions; a lighting characteristic calculation step of calculating a lighting characteristic value based upon the illumination-light source conditions and the indoor lighting environment conditions; and a correction step of executing correction processing that uses a color appearance model that is based upon the lighting characteristic value.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.